Conventionally, in the field of rechargeable secondary batteries, aqueous system batteries such as a lead battery, a nickel-cadmium battery, and a nickel-hydrogen battery were mainstream. However, along with reduction in size and weight of electrical devices, a lithium-ion secondary battery having a high energy density has begun to attract attention, and study, development, and commercialization thereof are now advanced rapidly. Further, under circumstances where global warming or exhaustion of resources come to light, an electric vehicle (EV) and a hybrid electric vehicle (HEV) having a mechanism where a driving force is partially assisted by an electric motor are developed by automobile manufacturers, and a secondary battery having large capacity and high output is required as a power supply for the EV and HEV.
As a power supply matching such requirements, a high voltage lithium-ion secondary battery of a non-aqueous system is now attracting attention. In particular, a rectangular lithium-ion secondary battery having a battery container with a flat-box shape has high volumetric efficiency when being packed and is thus increasingly demanded as a power supply to be mounted in the HEV, EV, or other equipment. In the rectangular secondary battery having such a sealed type battery container, a pressure inside the battery container may be increased due to, for example, overcharge, excessive temperature rise, or breakage by an external force.
There is known a non-aqueous electrolyte secondary battery provided with a current interrupting mechanism of interrupting current in the above case (see, for example, PTL 1). A non-aqueous electrolyte secondary battery described in PTL 1 has a fragile portion that is ruptured when a pressure inside an exterior can is increased to thereby interrupt electrical conduction. The fragile portion is connected, at its center portion, to a surface of a diaphragm that faces inside the battery, and a peripheral portion thereof is connected to a collector tab positioned below the diaphragm. When the diaphragm is deformed to be lifted up, the fragile portion is ruptured to interrupt electrical conduction to the diaphragm.